MIMO antenna module and MIMO antenna unit for distributed antenna system

ABSTRACT

An embodiment of an antenna module includes a substrate, a first antenna, and a second antenna. The first antenna is disposed on the substrate and is configured to radiate a first signal having a wavelength and a first polarization. And the second antenna is disposed on the substrate and is configured to radiate a second signal having the wavelength and a second polarization that is approximately orthogonal to the first polarization. For example, such an antenna module can include, as the first antenna, a T antenna configured to transmit and receive data that forms a first part of a MIMO-OFDM data symbol, and can include, as the second antenna, an F antenna configured to transmit and receive data that forms a second part of the MIMO-OFDM data symbol.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application No.62/635,981 filed on Feb. 27, 2018 and titled “MIMO ANTENNA MODULE ANDMIMO ANTENNA UNIT FOR DISTRIBUTED ANTENNA SYSTEM”, the contents of whichare incorporated herein in its entirety.

SUMMARY

Remote antenna units of a distributed antenna system (DAS) typically aredistributed within a structure (e.g., an office building, warehouse,mall) to provide wireless-communication coverage so that people can usetheir wireless devices while within the structure. Examples of the typesof wireless coverage that a DAS can provide include Wi-Fi®, and cellularand data service over one of the many available long-term-evolution(LTE) frequency bands (e.g., B1, B3, B7, B25, and B66). And thefrequency range over which the DAS can be configured to operate is, forexample, approximately 700 MHz-6000 MHz (6.00 GHz).

Because there are many available wireless-communication protocols andfrequency bands, it can be cost and time prohibitive to design, test,and manufacture a respective remote antenna unit for each possiblecombination of protocols and frequency bands that a designer may wish toinclude in a DAS.

Furthermore, to improve bandwidth and data-transfer speed as compared toa single-input-single-output (SISO) antenna unit, it can be desirable toincorporate multiple-input-multiple-output (MIMO) capability into aremote antenna unit. For example, it can be desirable to incorporateMIMO-orthogonal-frequency-division-multiplexing (MIMO-OFDM) capabilityinto a remote antenna unit.

But MIMO-OFDM antenna-spacing requirements can increase the size andform factor of a remote antenna unit beyond a desired size and formfactor, or, alternatively, can require locating the antennas remote fromthe main housing of the remote antenna unit. The latter is oftenundesirable because the need to connect remote antennas to the mainhousing can significantly increase the installation complexity of a DAS,and the medium (e.g., coaxial cables) used to couple the remote antennasto the main housing often introduces significant loss into thetransmitted and received signals.

Therefore, an embodiment of a remote antenna unit includes a commonbaseband module (hereinafter a controller module) and one or more radiomodules (hereinafter antenna modules) that are each configured forplug-and-play connection to the controller module at the time ofinstallation, and that are each configured for MIMO-OFDM operationaccording to at least one respective wireless protocol and for at leastone respective frequency band of the respective protocol. Furthermore,the multiple antennas associated with an antenna module are mounted to asubstrate (e.g., a circuit board) of the antenna module, and, therefore,are part of, not remote from, the antenna module.

By including a common (i.e., single-version) controller module, such aremote antenna unit promotes reduced design, manufacturing, and testingcosts as compared to the costs of designing, manufacturing, and testingmultiple versions of a controller module.

Furthermore, such a remote antenna unit allows one to custom design aDAS by acquiring radio modules configured to operate according todesired wireless protocols and in desired frequency bands, and byconnecting one or more of the acquired radio modules to each of thecontrol modules during installation of the DAS.

Moreover, by including MIMO-OFDM antennas that are mounted to a board ofthe antenna module and that are relatively close together (e.g., spacedapart by less than λ/2), such an antenna module allows the remoteantenna unit to have a reduced form factor and size as compared to anantenna unit having remote antennas, i.e., antennas that are not part ofthe antenna unit.

In addition, each version of the antenna module can be designed,manufactured, and tested independently of the common controller moduleand the other versions of the antenna module such that a change to oneversion of the antenna module, or an introduction of a new version ofthe antenna module, does not require redesigning, retesting, orrecertifying (e.g., for FCC compliance) the other existing versions ofthe antenna module.

An embodiment of such an antenna module includes a substrate, a firstantenna, and a second antenna. The first antenna is disposed on thesubstrate and is configured to radiate a first signal including awavelength and having a first polarization. And the second antenna isdisposed on the substrate and is configured to radiate a second signalincluding the same wavelength and having second polarization that isapproximately orthogonal to the first polarization.

For example, such an antenna module can include, as the first antenna,an F antenna configured to transmit and receive data that forms a firstMIMO-OFDM data symbol, and can include, as the second antenna, a Tantenna configured to transmit and receive data that forms a secondMIMO-OFDM data symbol.

And an embodiment of a remote antenna unit includes a controller moduleand one or more antenna modules. The controller module includes a firstsubstrate and at least one antenna-module connection region. And each ofthe at least one antenna module is configured for engagement with anantenna-module connection region of the control module, and includes arespective second substrate, a respective first antenna disposed on therespective second substrate and configured to radiate a respective firstsignal including a respective wavelength and having a respective firstpolarization, and a respective second antenna disposed on the respectivesecond substrate and configured to radiate a respective second signalincluding the same respective wavelength and having a respective secondpolarization that is approximately orthogonal to the respective firstpolarization.

For example, such a remote antenna unit allows one to connect theantenna modules to the controller module in a plug-and-play fashionduring installation of a DAS so that he/she can customize the remoteantenna unit, and, therefore, the DAS, without any special tools orset-up procedures. Furthermore, the controller module and antennamodules are configured such that when the one or more antenna modulesare properly engaged with the controller module, the controller moduleand one or more antenna modules can fit within a single housing having adesired form factor and size.

DRAWINGS

FIG. 1 is a diagram of a remote antenna unit that includes a controlmodule and four antenna modules, according to an embodiment.

FIGS. 2A and 2B are diagrams of a side view and of a top-down view,respectively, of a desired radiation pattern of the remote antenna unitof FIG. 1, according to an embodiment.

FIG. 3 is a bottom isometric view of an antenna module of FIG. 1,according to an embodiment.

FIG. 4 is a side view of a T-antenna assembly of FIG. 3, according to anembodiment.

FIG. 5 is a two-dimensional plot of the radiation pattern of the Tantenna of FIGS. 3-4, according to an embodiment.

FIG. 6 is a two-dimensional plot of the radiation pattern of the Fantenna of FIG. 3, according to an embodiment.

FIGS. 7A-7B are respective other two-dimensional plots of the radiationpattern of the T antenna of FIGS. 3-4, according to an embodiment.

FIGS. 8A-8B are respective other two-dimensional plots of the radiationpattern of the F antenna of FIG. 3, according to an embodiment.

FIG. 9 is a three-dimensional plot of the radiation pattern of the Tantenna of FIGS. 3-4, according to an embodiment.

FIG. 10 is a three-dimensional plot of the radiation pattern of the Fantenna of FIG. 3, according to an embodiment.

FIG. 11 is a plot of the envelope correlation coefficient, versusfrequency, between the T and F antennas of FIGS. 3-4, according to anembodiment.

FIG. 12 is a plot of the signal isolation, versus frequency, between theT and F antennas of FIGS. 3-4, according to an embodiment.

FIG. 13 is a plot of the diversity gain, versus envelope correlationcoefficient, for the T and F antennas of FIGS. 3-4, according to anembodiment.

FIG. 14 is bottom exploded view of the remote antenna unit of FIG. 1including multiple antenna modules of FIG. 3, according to anembodiment.

FIG. 15 is top exploded view of the remote antenna unit of FIGS. 1 and14 including multiple antenna modules of FIG. 3, according to anembodiment.

FIG. 16 is bottom view of the remote antenna unit of FIGS. 1 and 14-15including multiple antenna modules of FIG. 3, according to anembodiment.

FIG. 17 is a diagram of a distributed antenna system (DAS) thatincorporates one or more of the remote antenna units of FIGS. 1 and14-16, according to an embodiment.

FIG. 18 is a diagram of a centralized radio access network (C-RAN) thatincorporates one or more of the remote antenna units of FIGS. 1 and14-16, according to an embodiment.

DETAILED DESCRIPTION

“Approximately,” “substantially,” and similar words, as used herein,indicate that a given quantity b can be within a range b±10% of b, orb±1 if |10% of b|<1. “Approximately,” “substantially,” and similarwords, as used herein, also indicate that a range b−c can be fromb−0.10(c−b) to c+0.10(c−b). Regarding the planarity of a surface orother region, “approximately,” “substantially,” and similar words, asused herein, indicate that a difference in thickness between a highestpoint and a lowest point of the surface/region does not exceed 0.20millimeters (mm).

FIG. 1 is a diagram of a modular remote antenna unit 10 (sometimescalled a “remote transmit/receive module,” or a “remote unit”) of adistributed antenna system (DAS), according to an embodiment. Theantenna unit 10 includes a controller module 12 and one or more (herefour) MIMO-OFDM (here 2×2) antenna modules 14 ₁-14 ₄ configured forremovable attachment and electrical coupling to the controller module.The modularity of the antenna unit 10 allows one to design, manufacture,test, and certify (e.g., certify for FCC compliance) only a singleversion of the controller module 12, and allows him/her to customize theremote antenna unit 10, and, therefore, the DAS to which the remoteantenna unit belongs, by installing different versions of the antennamodules 14. That is, one who is charged with designing a DAS for aparticular structure can customize the DAS to operate according to oneor more desired wireless protocols and frequency bands by acquiring thecorresponding version of the antenna modules 14 and attaching theacquired antenna modules to the respective controller modules 12 duringinstallation of the DAS. For example, to customize a DAS system tosupport a Wi-Fi® protocol and the B1, B25, and B66 LTE bands, one couldattach, to each controller module 12, a respective Wi-Fi® antenna module14, a respective B1 antenna module, a respective B25 antenna module, anda respective B66 antenna module. The modularity of the remote antennaunit 10 also allows one to modify the remote antenna unit, and the DASto which it belongs, after installation by replacing one of more of theantenna modules 14 with other versions of the antenna modules.

Still referring to FIG. 1, the controller module 12 includes a substrate(e.g., a printed circuit board) 18, a control circuit 20 mounted to thesubstrate, an interface circuit 22 mounted to the substrate, andantenna-module connection regions 24 ₁-24 ₄ formed in the substrate.

The control circuit 20 is configured to control the antenna modules 14,the interface circuit 22, and other circuitry (not shown in FIG. 1) onboard the remote antenna unit 10. The control circuit 20 can be anysuitable type, or suitable combination, of a software-configurable,firmware-configurable, or hard-wired control circuit, such as amicroprocessor, microcontroller, field-programmable gate array (FPGA),and an application-specific integrated circuit (ASIC).

The interface circuit 22 is configured to communicate with a master unit(not shown in FIG. 1) of the DAS, and to provide power to the antennaunit 10. For example, the interface circuit 20 can include one or morePower-over-Ethernet (PoE) powered devices (PDs) 26 ₁-26 _(n), such as a1000BASE-T PoE-enabled powered device and a 2.5 GHz/5.0 GHz/10.0 GHzNBASE-T PoE-enabled powered device, can be configured to receive powerfrom power-source equipment (not shown in FIG. 1), and can be configuredto communicate with the master unit, via a suitable PoE cable (not shownin FIG. 1). In operation, the interface circuit 22 can communicate datafrom the master unit to one or more of the antenna modules 14 fortransmission, and can communicate data received from one or more of theantenna modules to the master unit.

And the antenna-module connection regions 24 are each configured toengage a connection region (described below) of an antenna module 14 sothat the antenna module is physically and electrically coupled to thecontroller module 12. As further described below in conjunction withFIGS. 14-16, each connection region 24 can be configured to couple aconductive region (hereinafter a “ground plane”) plane of the antennamodule 14 to a ground plane of the controller module 12.

Each antenna module 14 includes a controller-module connection region 28configured to engage an antenna-module connection region 24 of thecontroller module 12, includes multiple (here two) antennas 30, andincludes circuitry configured to transmit and to receive data via theantennas according to a MIMO-OFDM protocol. As described below inconjunction with FIGS. 14-16, the connection region 28 can be configuredto couple a ground plane of the antenna module 14 to a ground plane ofthe controller module 12. As described below in conjunction with FIGS.3-4 and 11-12, the antennas 30 of the antenna module 14 can beconfigured to have a suitably low envelope correlation coefficient and asuitably high level of signal isolation between them. Furthermore,during a transmit mode, the antenna-module circuitry is configured tosplit data received from the master unit (not shown in FIG. 1) via theinterface circuit 22 into two data symbols, one data symbol for each ofthe antennas 30, and to transmit the data symbols via the respectiveantennas according to a wireless protocol, and on a frequency band, forwhich the antenna module 14 is configured. And during a receive mode,the antenna-module circuitry is configured to recover, and to provide tothe master unit via the interface circuit 22, data symbols respectivelyreceived from the antennas 30 according to a wireless protocol, and on afrequency band, for which the antenna module 14 is configured. Because aMIMO-OFDM protocol calls for each of the antennas 30 of the antenna unit14 to transmit and to receive on a same frequency band and using a sameset of subcarrier frequencies, signals transmitted by the antennastypically include at least one same wavelength, and signals received bythe antennas typically include at least one same wavelength.

Still referring to FIG. 1, alternate embodiments of the remote antennaunit 10 are contemplated. For example, the antenna unit 10 can be otherthan a remote antenna unit of a DAS. Furthermore, the antenna unit 10can omit some of the above-described components, and can includecomponents not described. Moreover, one or more of the antenna modules14 can be other than a 2×2 MIMO-OFDM module. In addition, alternateembodiments described in conjunction with FIGS. 2-17 may be applicableto the remote antenna unit 10.

FIGS. 2A and 2B are a side view and a top view, respectively, of aradiation pattern 42, which the antennas 30 (FIG. 1) of the remoteantenna unit 10 are configured to form, according to an embodiment. Thatis, each set of antennas 30 of each of the antenna modules 14 isconfigured, at least ideally, to form the radiation pattern 42. Forexample, the antennas 30 ₁-30 ₂ of the antenna module 14 ₁ areconfigured to form, at least ideally, the radiation pattern 42, theantennas 30 ₃-30 ₄ of the antenna module 142 are configured to form, atleast ideally, the radiation pattern 42, the antennas 30 ₅-30 ₆ of theantenna module 14 e are configured to form, at least ideally, theradiation pattern 42, and the antennas 30 ₇-30 ₈ of the antenna module14 ₄ are configured to form, at least ideally, the radiation pattern 42.

Referring to FIG. 2A, the remote antenna unit 10 is typically mountedto, or inside of, a ceiling 40 of the structure in which it isinstalled.

Furthermore, the radiation pattern 42 has a higher gain near EL=90°, anda lower gain near EL=0°. Because of the higher gain near EL=90°, theradiation pattern 42 provides sufficient signal power to a wirelessdevice 44 located some non-zero horizontal distance away from theantenna unit 10. And even with a lower gain near EL=0°, the radiationpattern 42 still provides sufficient signal power to a wireless device46 located approximately directly under the antenna unit 10 because thedistance between the antenna unit and wireless device 46 is relativelysmall. For example, the radiation pattern 42 can provide a maximum gainwithin an approximate ranges of 270°≤EL≤345° and 15°≤EL≤90°.

And referring to FIG. 2B, in a plane approximately parallel to theceiling 40 (FIG. 2A), the radiation pattern 42 is, ideally,omni-directional, i.e., the radiation pattern 42 is, ideally,omni-directional in the azimuth dimension.

Still referring to FIGS. 2A-2B, alternate embodiments of the radiationpattern 42 are contemplated. For example, the antennas 30 of the antennaunit 10 can be configured to generate any suitable radiation patternother than the radiation pattern 42. In addition, alternate embodimentsdescribed in conjunction with FIGS. 1 and 3-17 may be applicable to theradiation pattern 42.

FIG. 3 is a bottom isometric view of an antenna module 14 of FIG. 1,according to an embodiment in which the two MIMO-OFDM antennas 30 ofFIG. 1 are a T antenna and an F antenna, respectively.

FIG. 4 is a side view of the T-antenna substrate 50 of the antennamodule 14 of FIG. 3, and of the T antenna 52 disposed on the T-antennasubstrate, according to an embodiment.

Referring to FIG. 3, in addition to the connection region 28 and theT-antenna substrate 50, the antenna module 14 includes an antenna-modulesubstrate 54, a signal connector 56, a heatsink 58, ground-planecontacts 60, circuitry (not shown in FIG. 3), and an F antenna 62.

The T antenna 52 and the F antenna 62, in the described embodiment, arethe antennas 30 of FIG. 2.

The connection region 28 is a slot that is configured to receive andengage a connection region 24 of FIG. 1, where the connection region 24includes a corresponding portion of the substrate 18 of the controllermodule 12 of FIG. 1. By engaging a corresponding portion of thesubstrate 18, the connection region 28 facilitates good electricalcontact between the ground plane (described below) of the substrate 18and the ground plane (described below) of the substrate 50, such thatthe antennas 52 and 62 of the antenna module 14 effectively “see” oneground plane. Without good electrical contact between the ground planes,the radiation patterns of the antennas 52 and 62 can differsignificantly from their designed parameters.

The antenna-module substrate 54 can be any type of suitable substrate,such as a printed-circuit board, and includes a conductive region 64,which is called a ground region or plane if, as is here, the conductiveregion is grounded. Although shown as being the bottom external layer ofthe substrate 54, the ground plane 64 can be in inner layer or the toplayer of the substrate. Furthermore, the substrate 54, and thus theground plane 64, lie approximately in the x-y plane. Moreover, if theground plane 64 is the bottom layer of the substrate 54, then thesubstrate can include a layer of an electric insulator over the groundplane to prevent short circuits to ground.

The signal connector 56 can be any suitable connector configured forengaging with a corresponding connector (not shown) on the controllermodule 12 of FIG. 1 to couple signals (e.g., data signals fortransmission, received data signals, power and ground signals) betweenthe circuitry onboard the antenna module 14 and the circuitry on thecontroller module.

The heat sink 58 is configured to dissipate heat generated by thecircuitry and the antennas 52 and 62 of the antenna module 14, and todissipate heat generated by the controller module 12 (FIG. 1) while theantenna module is coupled to the controller module. The heat sink 58 canbe formed from any suitable material (e.g., a metal such as aluminum)and can have any suitable shape.

The ground-plane contacts 60 are configured to couple, electrically, theground plane of the substrate 18 of the controller module 12 (FIG. 1) tothe ground plane 64 while the connector region 28 is engaged with aconnector region 24 (FIG. 1) of the controller module. The ground-planecontacts 60 can have any suitable composition and structure; forexample, each of the ground-plane contacts can be a respective D-shapedspring contact made from beryllium. Furthermore, the substrate 54 caninclude conductive vias for coupling the ground-plane contacts 60 to theground plane 64.

The antenna-module circuitry (not shown in FIG. 3) is disposed to a sideof the antenna-module substrate 54 opposite to the side on which the Tand F antennas 52 and 62 are disposed, and is configured to performfunctions such as error encoding and MIMO-OFDM encoding data,modulating, with the encoded data, subcarrier signals and a carriersignal for transmission, demodulating received carrier signals, andMIMO-OFDM decoding and error decoding received data. The antenna-modulecircuitry can include, for example, software-configurable circuitry suchas a microprocessor or micro controller, firmware-configurable circuitrysuch as a field-programmable gate array (FPGA), hardwired circuitry, ora subcombination or combination of software-configurable,firmware-configurable, and hardwired circuitry.

The F antenna 62 (also referred to as an inverted-F antenna (IFA) or aprinted-F antenna (PFA)) depending on its orientation relative to theviewer) includes conductors 68, 70, and 72 disposed on theantenna-module substrate 54 adjacent to, and in approximately the sameplane as, the ground plane 64. Because it is disposed approximatelycoplanar with the ground plane 64, the F antenna 62 allows the antennamodule 14, and, therefore, the antenna unit 10 (FIG. 1), to have arelatively low height (i.e., a relatively low profile) as describedbelow.

The conductor 68 of the F antenna 62 is approximately λ/4 long, where λ,is the center frequency of the frequency band for which the antennamodule 14 is configured.

The conductor 70 of the F antenna 62 is coupled to the antenna-modulecircuitry by a signal-feed node 74, a signal-feed trace 76, and athrough-substrate via 78. In series with the signal-feed trace 76 can bedisposed circuitry configured to match, approximately, the impedance“seen” by the antenna 62 to the impedance of the antenna.

The conductors 70 and 72 of the F antenna 62 can have any suitablelength, such as less than λ/8. Furthermore, the minimum width of theground plane 64, as measured from the end of the conductor 72 in contactwith the ground plane, is approximately λ/4, although in the describedembodiment, this width of the ground plane is >>λ/4. In an embodiment inwhich a designer wishes to maintain the sizes of the F antenna 62relatively consistent from one version of the antenna module 14 toanother version of the antenna module, the dimensions of the conductors70 and 72, and other dimensions of and distances within the antennamodule, may be fractions of λ that are different from those fractionsdescribed above depending on the frequency band(s) for which an antennamodule is configured.

The signal that the F antenna 62 is configured to transmit (hereinafter“radiate”) has an electric field (hereinafter “E-field”) that isgenerally in the x dimension, i.e., that is approximately perpendicularto the conductor 68, and that is approximately parallel to theconductors 70 and 72. That is, the E-field polarization of the signal,and, therefore, the E-field polarization of the F antenna 62, isgenerally in the x dimension, although the E-field polarization of thesignal and F antenna may also have a component in they dimension. Asdescribed below, this E-field polarization is configured to provide asuitably high level of isolation (i.e., a suitably low level ofinductive and capacitive coupling), and a suitably low envelopecorrelation coefficient, between the T antenna 52 and the F antenna 62,and, therefore, is configured to allow the T and F antennas to be spacedapart by less than λ/2.

Furthermore, the F antenna 62 is configured to receive an incomingsignal having an E-field component in the x dimension; if an incomingsignal has no E-field component approximately in the x dimension, thenthe signal is orthogonal to the primary polarization of the F antenna62, which, therefore, may be unable to receive the incoming signal witha suitable gain.

And, ideally, the F antenna 62 is configured to generate anomni-directional radiation pattern, such as the radiation pattern 42 ofFIGS. 2A-2B; actual examples of the radiation pattern of the F antenna62 are described below in conjunction with FIGS. 6, 8A-8B, and 10.

Referring to FIGS. 3-4, the T-antenna substrate 50 is attached to theantenna-module substrate 54 via tabs 80, 82, and 84. The tabs 80 and 84function to hold the T-antenna substrate 50 to the antenna-modulesubstrate 54, and the tab 82 functions to hold the T-antenna substrateto the antenna-module substrate and to electrically couple the T antenna52 to the antenna-module circuitry via a signal-feed trace 86 and inputvia 88 disposed on the substrate 54. In series with the signal-feedtrace 86 can be disposed circuitry configured to match, approximately,the impedance “seen” by the T antenna 52 to the impedance of theantenna.

The T antenna 52 includes conductors 90, 92, and 94, where theconductors 90 and 94 are disposed along an edge 96 of the T-antennasubstrate 50, and the conductor 92 is disposed approximately in thecenter of, and is approximately perpendicular to, the conductors 90 and94. Furthermore, the antenna-module circuitry drives the conductor 92 ofthe T antenna 52 with a signal to be transmitted, and receives incomingsignals from the conductor 92 of the T antenna, via the conductive tab82, which electrically couples the conductor 92 to the antenna-modulecircuitry (not shown in FIG. 3) on the opposite side of theantenna-module substrate 54.

In general, the T antenna 52 operates like a λ/4 monopole antennadisposed over a ground plane (the conductor 92 radiates acurrent-generated signal into the far field), but the conductors 90 and94 add capacitance, which allows the conductor 92 to be shorter than aλ/4 monopole antenna, with the tradeoff that the bandwidth of a Tantenna configured for operation at a particular center frequency istypically less than the bandwidth of a λ/4 monopole antenna configuredfor operation at the same center frequency. For example, the lengths ofthe conductors 90 and 94 can be set such that the height of theconductor 92 can be no more than approximately seventeen millimeters(mm), regardless of the frequency band for which the T antenna 52 isconfigured, to allow the antenna module 14 to have a desired height andprofile.

The signal that the T antenna 52 is configured to radiate has an E fieldthat is in the z dimension, i.e., has an E field that is approximatelyparallel to the conductor 92, and that is approximately perpendicular tothe conductors 90 and 94. That is, the E-field polarization of thesignal, and, therefore, of the T antenna 52, is in the z dimension. Asdescribed below, this E-field polarization provides a suitably highlevel of isolation (i.e., a suitably low level of inductive andcapacitive coupling), and a suitably low envelope correlationcoefficient, between the T antenna 52 and the F antenna 62, and,therefore, is configured to allow the T and F antennas to be spacedapart by less than λ/2 (the T and F antennas also can be spaced apart byλ/2 or by more than λ/2).

Furthermore, the T antenna 52 is configured to receive an incomingsignal having an E-field component in the z dimension; if an incomingsignal has no E-field component approximately in the z dimension, thenthe incoming signal is approximately orthogonal to the T antenna 52,which, therefore, may be unable to receive the incoming signal with asuitable gain.

And, ideally, the T antenna 52 is configured to generate anomni-directional radiation pattern, such as the radiation pattern 42 ofFIGS. 2A-2B; actual examples of the radiation pattern of the T antenna52 are described below in conjunction with FIGS. 5, 7A-7B, and 9.

Still referring to FIGS. 3-4, because the E-field polarizations of the Tantenna 52 and the F antenna 62 are approximately orthogonal to oneanother, the levels of inductive (mutual) and capacitive couplingbetween the T and F antennas is relatively low, ideally zero, and thelevel of isolation between the T and F antennas is relatively high,ideally infinite.

A relatively high isolation means that the T antenna 52 receives little,if any, energy from a signal radiated by the F antenna 62, and that theF antenna receives little, if any, energy from a signal radiated by theT antenna. Said another way, a signal radiated by the T antenna 52causes little or no interference with a signal received by the F antenna62, and a signal radiated by the F antenna causes little or nointerference with a signal received by the T antenna.

Furthermore, a relatively high isolation means that T antenna 52 hasrelatively little, if any, effect on the radiation pattern of the Fantenna 62, and that the F antenna has relatively little, if any, effecton the radiation pattern of the T antenna; said another way, arelatively high isolation renders the F and T antennas substantiallyindependent from one another.

Another benefit of a relatively high level of isolation is that the Tantenna 52 and the F antenna 62 can be spaced apart by less than λ/2.According to the Diffraction Theorem and the Wave Number Theorem, fortwo antennas that have similar radiation characteristics to appear asindependent radiators in the far field, they should be spaced apart byat least λ/2. But because the T antenna 52 and the F antenna 62 have arelatively high level of isolation between them, they can, at least insome applications, appear as independent radiators in the far field evenif they are spaced apart by less than λ/2. The ability to space the Tantenna 52 and the F antenna 62 apart by less than λ/2 allows areduction in the size of the antenna module 14, and of the antenna unit10 (FIG. 1), as compared to antenna modules and antenna units havingMIMO-OFDM antenna pairs spaced apart by at least λ/2.

Yet another benefit of a relatively high level of isolation is that theT antenna 52 and the F antenna 62 are relatively highly de-correlatedfrom one, another, i.e., the envelope correlation coefficient betweenthe T and F antennas is relatively small. MIMO-OFDM techniques rely onthe channels over which the T and F antennas 52 and 62 transmit andreceive signals exhibiting spatial diversity. For relatively longchannels, the spatial diversity typically is provided by the respectivemultiple paths of different distances that form each of the channels;that is, the spatial diversity is due to multipath. But for relativelyshort channels, such is where a wireless device 46 (FIG. 2A) is directlybelow the antenna unit 10 (FIG. 2A), multipath alone may not provide asufficient level of spatial diversity. But configuring the T and Fantennas 52 and 62 to have a relatively small envelope correlationcoefficient can provide a suitable level of spatial diversity even overrelatively short channels.

And a benefit of configuring the antenna module 14 for operation overonly a given one or more frequency bands is that the T and F antennas 52and 62 can be relatively narrow-band antennas, which typically have moreuniform in-band radiation patterns versus wavelength than do antennasthat are relatively wide-band antennas.

Still referring to FIGS. 3-4, in summary, the T antenna 52 and the Fantenna 62 are configured, and are oriented relative to one another,such that the level of isolation between the T and F antennas isrelatively high (ideally infinite), and such that the envelopecorrelation coefficient for the T and F antennas is relatively small(ideally zero).

FIG. 5 is a two-dimensional plot of the radiation pattern 100 of the Tantenna 52 of FIGS. 3-4 in the x-y plane of FIG. 3 over an approximatefrequency range of 1700 to 2200 MHz, according to an embodiment. Theradiation pattern 100 is approximately a dipole-type omni-directional asis desired for at least some applications of the antenna unit 10 asdescribed above in conjunction with FIG. 2B.

FIG. 6 is a two-dimensional plot of the radiation pattern 102 of the Fantenna 62 of FIG. 3 in the x-y plane of FIG. 3 over an approximatefrequency range of 1700 to 2200 MHz, according to an embodiment. Theradiation pattern 102 is approximately omni-directional as is desiredfor at least some applications of the antenna unit 10 as described abovein conjunction with FIG. 2B.

FIGS. 7A-7B are respective two-dimensional plots of the radiationpattern 100 of the T antenna 52 of FIGS. 3-4 in the y-z and x-z planesof FIG. 3 over an approximate frequency range of 1700 to 2200 MHz,according to an embodiment. The radiation pattern 100 has lower gain atelevation angles EL=0° (directly under the antenna unit 10) and EL=180°(directly over the antenna unit) as is desired for at least someapplications of the antenna unit as described above in conjunction withFIGS. 2A-2B.

FIGS. 8A-8B are respective two-dimensional plots of the radiationpattern 102 of the F antenna 62 of FIG. 3 in the y-z and x-z planes ofFIG. 3 over an approximate frequency range of 1700 to 2200 MHz,according to an embodiment. The radiation pattern 102 has lower gain atelevation angles EL=0° (directly under the antenna unit 10) and EL=180°(directly over the antenna unit) as is desired for at least someapplications of the antenna unit as described above in conjunction withFIGS. 2A-2B.

FIG. 9 is a three-dimensional plot of the radiation pattern 100 of the Tantenna 52 of FIGS. 3-4 at a frequency of 2 GHz, according to anembodiment.

FIG. 10 is a three-dimensional plot of the radiation pattern 102 of theF antenna 52 of FIG. 3 at a frequency of 2 GHz, according to anembodiment.

FIG. 11 is a plot 110 of the envelope correlation coefficient versusfrequency between the T antenna 52 and the F antenna 62 of FIG. 3,according to an embodiment. At a frequency of approximately 1.75 GHz,and at frequencies above approximately 2.08 GHz, the envelopecorrelation coefficient is less than 0.1, which is suitable for mostMIMO applications. And for all frequencies except frequencies within theapproximate frequency band of 1.88 GHz-1.98 GHz, the error correctioncoefficient is no greater than 0.3, which is suitable for many MIMOapplications.

FIG. 12 is a plot 120 of the isolation (in decibels (dB)) between the Tantenna 52 and the F antenna 62 of FIG. 3, according to an embodiment.For frequencies within an approximate frequency band of 1.42 GHz-2.5GHz, the isolation is no less than about 23 dB, which is suitable formost MIMO applications.

FIG. 13 is a plot 130 of the MIMO-OFDM diversity gain (in dB) versusenvelope correlation coefficient for the combination of the T antenna 52and the F antenna 62 of FIG. 3, according to an embodiment. Diversitygain is the apparent gain of the MIMO-OFDM pair of antennas 52 and 62over the gain of a single one of these antennas. That is, assuming theindividual gains of the T antenna 52 and the F antenna 62 areapproximately equal and normalized to unity, the diversity gain is ameasure of how many times greater is the apparent gain of the MIMO-OFDMpair of antennas than the gain of a single one of the antennas. Forexample, a diversity gain of 10 dB indicates that the gain of theMIMO-OFDM pair of antennas 52 and 62 is 10 dB greater than the gain ofthe one of the T and F antennas having the highest individual gain. Inthe described embodiment, the diversity gain is an approximatelyconstant 10 dB, and the bit-error rate (BER) is approximately 1.0%, forenvelope correlation coefficients up to approximately 0.3; a 10 dBdiversity gain and a 1.0% BER is suitable for many MIMO-OFDMapplications.

Referring again to FIGS. 3-4, operation of the antenna module 14, whileit is connected to the controller module 12 (FIG. 1), is described,according to an embodiment in which the antenna module transmits andreceives signals using a MIMO-OFDM technique.

During signal transmission, a remote source, such as a master unit of aDAS, sends data to the antenna module 14 via one or more pins, or othercontacts, of the signal connector 56.

The antenna-module circuitry generates, and transmits via the T and Fantennas 52 and 62, respective training symbols so that one or moreremote (from the antenna module 14) receivers (not shown in FIGS. 3-4)can characterize the respective channels over which the T and F antennasare transmitting respective signals.

The antenna-module circuitry also splits the data into two data symbols,one for each of the T antenna 52 and F antenna 62.

The antenna-module circuitry then error encodes each of the datasymbols.

The antenna-module circuitry next MIMO-OFDM encodes the error-encodeddata symbols, and modulates, with respective portions of the datasymbols, a number (e.g., 512, 1024) of orthogonal subcarrier signalswithin the frequency band for which the antenna-module 14 is configured.That is, the antenna-module circuitry generates a first set ofsubcarrier signals modulated with one of the data symbols, and generatesa second set of subcarrier signals, at the same frequencies as the firstset of subcarrier signals, modulated with the other of the data symbols.Example subcarrier-modulation techniques include Quadrature Phase-ShiftKeying (QPSK) and Quadrature Amplitude Modulation (QAM) such as QAM-16and QAM-64.

The antenna circuitry then performs, on each of the first and secondsets of modulated subcarrier signals, an inverse fast Fourier Transform(IFFT), to generate respective first and second transmission datasignals.

The antenna circuitry next modulates each of two carrier signals with arespective one of the first and second transmission data signals.

The antenna circuitry then provides the carrier signal modulated withthe first transmission data signal to one of the T antenna 52 and Fantenna 62 for transmission, and provides the carrier signal modulatedwith the second transmission data signal to the other of the T antennaand F antenna for transmission.

As described above in conjunction with FIGS. 3-4 and 13, because of therelatively high-diversity gain (e.g., 10 dB) exhibited by the T and Fantennas 52 and 62, a receiver can recover the first and second datasymbols from the received modulated carrier signals even though thefirst and second transmission data signals include the same subcarrierfrequencies, and even if the T and F antennas are spaced apart by lessthan λ/2 (λ can be the center wavelength of the frequency band, or thelongest wavelength of the frequency band).

Still referring to FIGS. 3-4, during signal reception from a remoteMIMO-OFDM transmitter, the antenna-module circuitry demodulates therespective signals received by the T and F antennas 52 and 62 to recoverfirst and second received data signals.

The antenna-module circuitry then subjects each of the first and secondreceived data signals to a fast Fourier Transform (FFT), and recoversvalues carried by the modulated subcarriers of each of the received datasignals.

The antenna-module circuitry next recovers, from the values, the twoencoded data symbols generated and transmitted by the remotetransmitter.

The antenna-module circuitry then MIMO-OFDM and error-correction decodesthe recovered encoded data symbols to recover the two data symbolstransmitted by the remote transmitter.

Referring to FIGS. 3-13, alternate embodiments of the antenna-module 14are contemplated. For example, the antennas 52 and 62 can be other thanT and F antennas. In addition, alternate embodiments described inconjunction with FIGS. 1-2B and 14-17 can be applicable to theantenna-module 14.

FIG. 14 is an exploded bottom view of the antenna unit 10 of FIG. 1,according to an embodiment.

FIG. 15 is an exploded top view of the antenna unit 10 of FIGS. 1 and14, according to an embodiment.

FIG. 16 is a bottom view of an assembled and fully populated (withantenna modules 14) antenna unit 10 of FIGS. 1 and 14-15, according toan embodiment.

Referring to FIGS. 14 and 16, the controller module 12 includes aconductive region, e.g., a ground plane, 140, which forms an outerconductive layer of the substrate 18. The ground plane 140 can be fullyexposed, or can be covered with an electric insulator and exposed onlyin one or more regions configured for engagement with the ground-planecontacts 60 of the antenna modules 14. Alternatively, the ground plane140 can an inner conductive layer of the substrate 18, which can includevias for coupling the ground plane to the ground-plane contacts 60.

Referring to FIG. 14, the connection region 24 of the controller module12 is configured to slide into, and engage, the connection region 28 ofa respective antenna module 14. Once the connections regions 24 and 28are engaged, the ground-plane contacts 60 contact one or more exposedportions (not shown in FIG. 14) of the ground plane 140 of thecontroller module 12 to provide a low-impedance coupling of the groundplane 140 with the ground plane 54 of the antenna module 14. Such alow-impedance coupling allows the T and F antennas 52 and 62 to “see”one large ground plane such that each of the antennas has a respectiveradiation pattern for which it is configured (an antenna that does not“see” such a large ground plane can exhibit a degraded radiationpattern).

Referring to FIG. 15, the signal connector 56 of each antenna module 14is configured to engage a respective signal connector (not shown in FIG.15) disposed on the controller module 12.

Referring to FIG. 16, the assembled, and fully populated (with antennamodules 14), antenna unit 10 is configured to fit into a singleenclosure (not shown in FIGS. 14-16) that is no larger thanapproximately 12 inches×10 inches×2 inches. That is, after one assemblesthe antenna unit 10, he/she can insert the antenna unit into such anenclosure, which, although not shown in FIGS. 14-16, can include/exposeconnectors 144 (e.g., PoE) for power and communication with a masterunit of a DAS. And the enclosure can include a radome that covers thebottom side (the side with the T and F antennas 52 and 62) of theantenna unit 10.

Furthermore, the antenna modules 14 are spaced apart from one another byrespective distances that are sufficient to provide a sufficient levelof isolation between antennas of different antenna modules. Because, asdescribed above in conjunction with FIGS. 3-4, the polarizations of theT and F antennas 52 and 62 are orthogonal to one another, the T antennaof one antenna module 14 typically is sufficiently isolated from the Fantenna of another antenna module regardless of the distance between theantenna modules; similarly, the F antenna of one antenna moduletypically is sufficiently isolated from the T antenna of another antennamodule regardless of the distance between the antenna modules. And eventhough the polarizations of T antennas 52 of different antenna modules14, and the polarizations of F antennas 62 of different antenna modules,are approximately aligned with one another, the antenna modules arespaced apart by distances that provide a sufficient level of isolationbetween like antennas on different antenna modules. For example, anantenna-module separation distance in the approximate range of λ/4-λ/2has been found to provide a suitable level of isolation (e.g., >15 dB),where λ, is the center wavelength (or longest wavelength) of thelowest-frequency band supported by any version of antenna units 14.

Moreover, if multiple antenna units 14 are configured to transmit andreceive on a same frequency band, then the control circuit 20 (FIG. 1)of the controller module 12 can be configured to cause each of theseantenna units to use a respective set of subcarriers to avoid signalinterference between antenna modules.

Referring to FIGS. 14-16, due to the design of the connections regions24 and 28 and the signal connector 56, one can install and remove anantenna module 14 to/from the controller module 12 quickly and easilywithout the need for complicated instructions, and without the need fortools and specialized procedures. Alternatively, one can secure anantenna module 14 to the controller module 12 with optional screws 146and a standard Philip's head or flat-head screwdriver (not shown inFIGS. 14-16).

Furthermore, because the controller module 12 has only a single version,and, therefore, is common to all versions of the antenna units 14, oneneed not match a version of an antenna unit to a version of a controllermodule, or vice-versa. This can save costs, because only one version ofthe controller module 12 need be purchased and inventoried by a systemowner, and it can save time because an installer need not waste timeinadvertently installing an incorrect version of the controller moduleand then re-installing the correct version.

Still referring to FIGS. 14-16, alternate embodiments of the antennaunit 10 are contemplated. For example, although described as being fullypopulated with antenna units 14, the antenna unit 10 can be onlypartially populated. Furthermore, although described as being configuredto engage four antenna modules 14, the antenna unit 10 can be configuredto engage fewer than, or more than, four antenna modules. Moreover,although all of the antenna modules 14 are described as having a sameantenna configuration (e.g., type, number, orientation of antennas), oneor more of the antenna modules can have a different antennaconfiguration than one or more of the other antenna modules. Inaddition, alternate embodiments described in conjunction with FIGS. 1-13and 17 may be applicable to the antenna unit 10.

FIG. 17 is a block diagram of a distributed antenna system (DAS) 160,which can include one or more of the remote antenna units 10 of FIGS.1-2B and 14-16, according to an embodiment. In the described example, atleast one of the remote antenna units 10 of the DAS 160 includes atleast one antenna module 14 of FIG. 3.

The DAS 160 includes one or more master units 162 and one or more remoteantenna units 10 that are communicatively coupled to the master units162. Further in this embodiment, the DAS 160 includes a digital DAS, inwhich DAS traffic is distributed between the master units 162 and theremote antenna units 10 in digital form. In other embodiments, the DAS160 is implemented, at least in part, as an analog DAS, in which DAStraffic is distributed at least part of the way between the master units162 and the remote antenna units 10 in analog form.

Each master unit 162 is communicatively coupled to one or more basestations 166. One or more of the base stations 166 can be co-locatedwith the respective master unit 162 to which it is coupled (for example,where the base station 166 is dedicated to providing base stationcapacity to the DAS 160). Also, one or more of the base stations 166 canbe located remotely from the respective master unit 162 to which it iscoupled (for example, where the base station 166 is a macro base stationproviding base station capacity to a macro cell in addition to providingcapacity to the DAS 160). In this latter case, a master unit 162 can becoupled to a donor antenna in order to wirelessly communicate with theremotely located base station 166.

The base stations 166 can be implemented as traditional monolithic basestations. Also, the base stations 166 can be implemented using adistributed base station architecture in which a base band unit (BBU) iscoupled to one or more remote radio heads (RRHs), where the front haulbetween the BBU and the RRH uses streams of digital IQ samples. Examplesof such an approach are described in the Common Public Radio Interface(CPRI) and Open Base Station Architecture Initiative (OBSAI) families ofspecifications.

The master units 162 can be configured to use wideband interfaces ornarrowband interfaces to the base stations 166. Also, the master units162 can be configured to interface with the base stations 166 usinganalog radio frequency (RF) interfaces or digital interfaces (forexample, using a CPRI or OBSAI digital IQ interface).

Traditionally, each master unit 162 interfaces with each base station166 using the analog radio frequency signals that each base station 166communicates to and from mobile units 168 using a suitable air interfacestandard. The DAS 160 operates as a distributed repeater for such radiofrequency signals. RF signals transmitted from each base station 166(also referred to herein as “downlink RF signals”) are received at oneor more master units 162. Each master unit 162 uses the downlink RFsignals to generate a downlink transport signal that is distributed toone or more of the remote units 164. Each such remote antenna unit 10receives the downlink transport signal and reconstructs a version of thedownlink RF signals based on the downlink transport signal and causesthe reconstructed downlink RF signals to be radiated from at least oneantenna array 170 (e.g., at least one array of the T and F antennas 52and 56 of FIGS. 3-4 and 14-16) coupled to or included in that remoteantenna unit 10.

A similar process is performed in the uplink direction. RF signalstransmitted from mobile units 168 (also referred to herein as “uplink RFsignals”) are received at one or more remote antenna units 10. Eachremote unit 10 uses the uplink RF signals to generate an uplinktransport signal that is transmitted from the remote unit 10 to a masterunit 162. Each master unit 162 receives uplink transport signalstransmitted from one or more remote units 10 coupled to it. The masterunit 162 combines data or signals communicated via the uplink transportsignals received at the master unit 162 and reconstructs a version ofthe uplink RF signals received at the remote units 10. The master unit162 communicates the reconstructed uplink RF signals to one or more basestations 166. In this way, the coverage of the base stations 166 can beexpanded using the DAS 160.

One or more intermediate units 170 (some of which are also referred tohere as “expansion units” 170) can be placed between the master units162 and one or more of the remote units 10. This can be done, forexample, in order to increase the number of remote units 10 that asingle master unit 162 can feed, to increase themaster-unit-to-remote-unit distance, and/or to reduce the amount ofcabling needed to couple a master unit 162 to its associated remoteunits 10.

As noted above, the DAS 160 is implemented as a digital DAS. In a“digital” DAS, signals received from and provided to the base stations166 and mobile units 168 are used to produce digital in-phase (I) andquadrature (Q) samples, which are communicated between the master units162 and remote units 10. It is important to note that this digital IQrepresentation of the original signals received from the base stations166 and from the mobile units 168 still maintains the originalmodulation (that is, the change in the amplitude, phase, or frequency ofa carrier) used to convey telephony or data information pursuant to thecellular air interface protocol used for wirelessly communicatingbetween the base stations 166 and the mobile units 168. Examples of suchcellular air interface protocols include, for example, the Global Systemfor Mobile Communication (GSM), Universal Mobile TelecommunicationsSystem (UMTS), High-Speed Downlink Packet Access (HSDPA), and Long-TermEvolution (LTE) air interface protocols. Also, each stream of digital IQsamples represents or includes a portion of wireless spectrum. Forexample, the digital IQ samples can represent a single radio accessnetwork carrier (for example, a UMTS or LTE carrier of 5 MHz) onto whichvoice or data information has been modulated using a UMTS or LTE airinterface. However, it is to be understood that each such stream canalso represent multiple carriers (for example, in a band of frequencyspectrum or a sub-band of a given band of frequency spectrum).

Furthermore, one or more of the master units 162 are configured tointerface with one or more base stations 166 using an analog RFinterface (for example, either a traditional monolithic base station 166or via the analog RF interface of an RRH). The base stations 166 can becoupled to the master units 162 using a network of attenuators,combiners, splitters, amplifiers, filters, cross-connects, etc.,(sometimes referred to collectively as a “point-of-interface” or “POI”).This is done so that, in the downstream, the desired set of RF carriersoutput by the base stations 166 can be extracted, combined, and routedto the appropriate master unit 162, and so that, in the upstream, thedesired set of carriers output by the master unit 162 can be extracted,combined, and routed to the appropriate interface of each base station166.

Each master unit 162 can produce digital IQ samples from an analogwireless signal received at radio frequency (RF) by down-converting thereceived signal to an intermediate frequency (IF) or to baseband,digitizing the down-converted signal to produce real digital samples,and digitally down-converting the real digital samples to producedigital in-phase (I) and quadrature (Q) samples. These digital IQsamples can also be filtered, amplified, attenuated, and/or re-sampledor decimated to a lower sample rate. The digital samples can be producedin other ways. Each stream of digital IQ samples represents a portion ofwireless radio frequency spectrum output by one or more base stations166. Each portion of wireless radio frequency spectrum can include, forexample, a band of wireless spectrum, a sub-band of a given band ofwireless spectrum, or an individual wireless carrier.

Likewise, in the upstream, each master unit 162 can produce an upstreamanalog wireless signal from one or more streams of digital IQ samplesreceived from one or more remote units 10 by digitally combining streamsof digital IQ samples that represent the same carriers or frequencybands or sub-bands (for example, by digitally summing such digital IQsamples), digitally up-converting the combined digital IQ samples toproduce real digital samples, performing a digital-to-analog process onthe real samples in order to produce an IF or baseband analog signal,and up-converting the IF or baseband analog signal to the desired RFfrequency. The digital IQ samples can also be filtered, amplified,attenuated, and/or re-sampled or interpolated to a higher sample rate,before and/or after being combined. The analog signal can be produced inother ways (for example, where the digital IQ samples are provided to aquadrature digital-to-analog converter that directly produces the analogIF or baseband signal).

One or more of the master units 162 can be configured to interface withone or more base stations 166 using a digital interface (in addition to,or instead of) interfacing with one or more base stations 166 via ananalog RF interface. For example, the master unit 162 can be configuredto interact directly with one or more BBUs using the digital IQinterface that is used for communicating between the BBUs and an RRHs(for example, using the CPRI serial digital IQ interface).

In the downstream, each master unit 162 terminates one or moredownstream streams of digital IQ samples provided to it from one or moreBBUs and, if necessary, converts (by re-sampling, synchronizing,combining, separating, gain adjusting, etc.) them into downstreamstreams of digital IQ samples compatible with the remote units 10 usedin the DAS 160. In the upstream, each master unit 162 receives upstreamstreams of digital IQ samples from one or more remote units 10,digitally combining streams of digital IQ samples that represent thesame carriers or frequency bands or sub-bands (for example, by digitallysumming such digital IQ samples), and, if necessary, converts (byre-sampling, synchronizing, combining, separating, gain adjusting, etc.)them into upstream streams of digital IQ samples compatible with the oneor more BBUs that are coupled to that master unit 162.

Each master unit 162 can be implemented in other ways.

In the downstream, each remote unit 10 receives streams of digital IQsamples from one or more master units 162, where each stream of digitalIQ samples represents a portion of wireless radio frequency spectrumoutput by one or more base stations 166.

Each remote unit 164 is communicatively coupled to one or more masterunits 162 using one or more ETHERNET-compatible cables 172 (for example,one or more CAT-6A cables). In this embodiment, each remote unit 10 canbe directly connected to a master unit 162 via a single ETHERNET cable172 or indirectly via multiple ETHERNET-compatible cables 172 such aswhere a first ETHERNET cable 172 connects the remote unit 10 to a patchpanel or expansion/intermediate unit 170 and a second optical fibercable 172 connects the patch panel or expansion/intermediate unit 170 tothe master unit 162. Each remote unit 10 can be coupled to one or moremaster units 162 in other ways. And the master unit 162 orexpansion/intermediate unit(s) 170 can include one or more PSEs 14(FIG. 1) that are configured to provide power to the remote units 10 asdescribed above in conjunction with FIGS. 1-3 and 14-16.

FIG. 18 is a block diagram of a centralized radio access network (C-RAN)180, which can include one or more of the remote antenna units 10 ofFIGS. 1-2B and 14-16, according to an embodiment. In the describedexample, at least one of the remote antenna units 10 of the C-RAN 180includes at least one antenna module 14 of FIG. 3. Furthermore,hereinafter the remote antenna units 10 are referred to as radio points(RPs) 186.

A centralized radio access network (C-RAN) is one way to implement basestation functionality. Typically, for each cell implemented by a C-RAN,a single baseband unit (BBU) interacts with multiple radio points inorder to provide wireless service to various items of user equipment(UEs).

FIG. 18 is a block diagram illustrating one exemplary embodiment of aradio access network (RAN) system 180 in which one or more remoteantenna units 10 of FIGS. 1-2B and 14-16, hereinafter referred to asradio points, or RPs, 186, can be implemented. The system 180 isdeployed at a site 182 to provide wireless coverage and capacity for oneor more wireless network operators. The site 182 may be, for example, abuilding or campus or other grouping of buildings (used, for example, byone or more businesses, governments, other enterprise entities) or someother public venue (such as a hotel, resort, amusement park, hospital,shopping center, airport, university campus, arena, or an outdoor areasuch as a ski area, stadium or a densely-populated downtown area).

In the exemplary embodiment shown in FIG. 18, the system 180 isimplemented at least in part using a C-RAN (point-to-multipointdistributed base station) architecture that employs at least onebaseband unit 184 and multiple radio points (RPs) 186 serve at least onecell 183. The system 180 is also referred to here as a “C-RAN system”180. The baseband units 184 are also referred to here as “basebandcontrollers” 184 or just “controllers” 184. Each RP 186 includes or iscoupled to one or more antennas 188 via which downlink RF signals areradiated to user equipment (UE) 190 and via which uplink RF signalstransmitted by UEs 190 are received.

More specifically, in the example shown in FIG. 18, each RP 186comprises two antennas 188. Each RP 186 can include or be coupled to adifferent number of antennas 188.

The system 180 is coupled to the core network 192 of each wirelessnetwork operator over an appropriate back-haul. In the exemplaryembodiment shown in FIG. 18, the Internet 194 is used for back-haulbetween the system 180 and each core network 192. However, it is to beunderstood that the back-haul can be implemented in other ways.

The exemplary embodiment of the system 180 shown in FIG. 18 is describedhere as being implemented as a Long Term Evolution (LTE) radio accessnetwork providing wireless service using an LTE air interface. LTE is astandard developed by 3GPP standards organization. In this embodiment,the controller 184 and RPs 186 together are used to implement an LTEEvolved Node B (also referred to here as an “eNodeB” or “eNB”) that isused to provide user equipment 190 with mobile access to the wirelessnetwork operator's core network 192 to enable the user equipment 190 towirelessly communicate data and voice (using, for example, Voice overLTE (VoLTE) technology).

Also, in this exemplary LTE embodiment, each core network 192 isimplemented as an Evolved Packet Core (EPC) 192 comprising standard LTEEPC network elements such as, for example, a mobility management entity(MME) (not shown) and a Serving Gateway (SGW) (not shown) and,optionally, a Home eNodeB gateway (HeNB GW) (not shown) and a SecurityGateway (SeGW) (not shown).

Moreover, in this exemplary embodiment, each controller 184 communicateswith the MME and SGW in the EPC core network 192 using the LTE S1interface and communicates with other eNodeBs using the LTE X2interface. For example, the controller 184 can communicate with anoutdoor macro eNodeB (not shown) via the LTE X2 interface.

Each controller 184 and the radio points 186 can be implemented so as touse an air interface that supports one or more of frequency-divisionduplexing (FDD) and/or time-division duplexing (TDD). Also, thecontroller 184 and the radio points 186 can be implemented to use an airinterface that supports one or more of themultiple-input-multiple-output (MIMO), single-input-single-output(SISO), single-input-multiple-output (SIMO),multiple-input-single-output (MISO), and/or beam forming schemes. Forexample, the controller 184 and the radio points 186 can implement oneor more of the LTE transmission modes. Moreover, the controller 184and/or the radio points 186 can be configured to support multiple airinterfaces and/or to support multiple wireless operators.

In the exemplary embodiment shown in FIG. 18, the front-haul thatcommunicatively couples each controller 184 to the one or more RPs 186is implemented using a standard

ETHERNET network 196. However, it is to be understood that thefront-haul between the controllers 184 and RPs 186 can be implemented inother ways.

Generally, one or more nodes in a C-RAN perform analog radio frequency(RF) functions for the air interface as well as digital Layer 1, Layer2, and Layer 3 (of the Open Systems Interconnection (OSI) model)functions for the air interface.

In the exemplary embodiment shown in (L1) FIG. 18, each basebandcontroller 184 comprises Layer-3 (L3) functionality 200, Layer-2 (L2)functionality 202, and Layer-1 (L1) functionality 204 configured toperform at least some of the Layer-3 processing, Layer-2 processing, andLayer-1 processing, respectively, for the LTE air interface implementedby the RAN system 180, and each RP 186 includes (optionally) Layer-1functionality (not shown) that implements any Layer-1 processing for theair interface that is not performed in the controller 184 and one ormore radio frequency (RF) circuits (not shown) that implement the RFfront-end functions for the air interface and the one or more antennas188 associated with that RP 186.

Each baseband controller 184 can be configured to perform all of thedigital Layer-3, Layer-2, and Layer-1 processing for the air interface,while the RPs 186 (specifically, the RF circuits) implement only the RFfunctions for the air interface and the antennas 188 associated witheach RP 186. In that case, IQ data representing time-domain symbols forthe air interface is communicated between the controller 184 and the RPs186. Communicating such time-domain IQ data typically requires arelatively high data rate front haul. This approach (communicatingtime-domain IQ data over the front haul) is suitable for thoseimplementations where the front-haul ETHERNET network 116 is able todeliver the required high data rate.

If the front-haul ETHERNET network 196 is not able to deliver the datarate needed to front haul time-domain IQ data (for example, where thefront-haul is implemented using typical enterprise-grade ETHERNETnetworks), this issue can be addressed by communicating IQ datarepresenting frequency-domain symbols for the air interface between thecontrollers 184 and the RPs 186. This frequency-domain IQ datarepresents the symbols in the frequency domain before the inverse fastFourier transform (IFFT) is performed. The time-domain IQ data can begenerated by quantizing the IQ data representing the frequency-domainsymbols without guard band zeroes or any cyclic prefix and communicatingthe resulting compressed, quantized frequency-domain IQ data over thefront-haul ETHERNET network 196. Additional details regarding thisapproach to communicating frequency-domain IQ data can be found in U.S.patent application Ser. No. 13/762,283, filed on Feb. 7, 2013, andtitled “RADIO ACCESS NETWORKS,” which is hereby incorporated herein byreference.

Where frequency-domain IQ data is front-hauled between the controllers184 and the RPs 186, each baseband controller 184 can be configured toperform all or some of the digital Layer-3, Layer-2, and Layer-1processing for the air interface. In this case, the Layer-1 functions ineach RP 186 can be configured to implement the digital Layer-1processing for the air interface that is not performed in the controller184.

Where the front-haul ETHERNET network 196 is not able to deliver thedata rate need to front haul (uncompressed) time-domain IQ data, thetime-domain IQ data can be compressed prior to being communicated overthe ETHERNET network 196, thereby reducing the data rate neededcommunicate such IQ data over the ETHERNET network 196.

Data can be front-hauled between the controllers 184 and RPs 186 inother ways (for example, using front-haul interfaces and techniquesspecified in the Common Public Radio Interface (CPRI) and/or Open BaseStation Architecture Initiative (OBSAI) family of specifications).

Each controller 184 and RP 186 (and the functionality described as beingincluded therein) can be implemented in hardware, software, orcombinations of hardware and software, and the various implementations(whether hardware, software, or combinations of hardware and software)can also be referred to generally as “circuitry” or a “circuit”configured to implement at least some of the associated functionality.When implemented in software, such software can be implemented insoftware or firmware executing on one or more suitable programmableprocessors. Such hardware or software (or portions thereof) can beimplemented in other ways (for example, in a field programmable gatearray (FPGA), application specific integrated circuit (ASIC), etc.).Also, the RF functionality can be implemented using one or more RFintegrated circuits (RFICs) and/or discrete components. Each controller184 and RP 186 can be implemented in other ways.

In the exemplary embodiment shown in FIG. 18, a management system 198 iscommunicatively coupled to the controllers 184 and RPs 186, for example,via the Internet 194 and ETHERNET network 196 (in the case of the RPs186).

In the exemplary embodiment shown in FIG. 18, the management system 198communicates with the various elements of the system 180 using theInternet 194 and the ETHERNET network 196. Also, in someimplementations, the management system 198 sends and receives managementcommunications to and from the controllers 184, each of which in turnforwards relevant management communications to and from the RPs 186.

Referring to FIGS. 17-18, alternate embodiments of the systems 160 and180 are contemplated.

The methods and techniques described herein may be implemented in analogelectronic circuitry, digital electronic circuitry, or with aprogrammable processor (for example, a special-purpose processor, ageneral-purpose processor such as a computer, a microprocessor, ormicrocontroller) firmware, software, or in combinations of them.Apparatuses embodying these techniques may include appropriate input andoutput devices, a programmable processor, and a storage medium tangiblyembodying program instructions for execution by the programmableprocessor. A process embodying these techniques may be performed by aprogrammable processor executing a program of instructions to performdesired functions by operating on input data and generating appropriateoutput. The techniques may advantageously be implemented in one or moreprograms that are executable on a programmable system including at leastone programmable processor coupled to receive data and instructionsfrom, and to transmit data and instructions to, a data storage system,at least one input device, and at least one output device. Generally, aprocessor will receive instructions and data from a read-only memoryand/or a random access memory. Storage devices suitable for tangiblyembodying computer program instructions and data include all forms ofnon-volatile memory, including by way of example semiconductor memorydevices, such as EPROM, EEPROM, and flash memory devices; magnetic diskssuch as internal hard disks and removable disks; magneto-optical disks;and DVD disks. Any of the foregoing may be supplemented by, orincorporated in, specially-designed application-specific integratedcircuits (ASICs).

Example Embodiments

Example 1 includes an antenna module, comprising: a first substrate; afirst antenna disposed on the first substrate and configured to radiatea first signal having a wavelength and a first polarization; and asecond antenna disposed on the first substrate and configured to radiatea second signal having the wavelength and a second polarization that isapproximately orthogonal to the first polarization.

Example 2 includes the antenna module of Example lwherein the firstsubstrate includes a printed circuit board.

Example 3 includes the antenna module of any of Examples 1-2 wherein:the first substrate has an area and a conductive region that spans morethan half of the area; one of the first and second antennas is disposedadjacent to the conductive region; and the other of the first and secondantennas is disposed over the conductive region.

Example 4 includes the antenna module of any of Examples 1-3 wherein:one of the first and second antennas includes a conductive tracedisposed on the first substrate; and the other of the first and secondantennas is disposed on a second substrate that is disposed over, andelectrically coupled to, the first substrate.

Example 5 includes the antenna module of any of Examples 1-4 wherein:the one of the first and second antennas includes a T antenna; and theother of the first and second antennas includes an F antenna.

Example 6 includes the antenna module of any of Examples 1-5 wherein:the first substrate has an area and a conductive region that spans morethan half of the area and has an edge; and the T antenna is disposedover, and at least one fourth the wavelength from the edge of, theconductive region.

Example 7 includes the antenna module of any of Examples 1-6 wherein:one of the first and second antennas includes a T antenna; and the otherof the first and second antennas includes an F antenna.

Example 8 includes the antenna module of any of Examples 1-7 wherein:the first and second polarizations respectively include first and secondE-field polarizations; one of the first and second E-field polarizationsis approximately parallel to the substrate; and the other of the firstand second E-field polarizations is approximately orthogonal to thesubstrate.

Example 9 includes the antenna module of any of Examples 1-8 wherein thesecond antenna is spaced from the first antenna by a distance that isless than one half the wavelength.

Example 10 includes an antenna unit, comprising: a control moduleincluding a first substrate and at least one antenna-module connectionregion; and at least one antenna module each configured for engagementwith an antenna-module connection region of the control module, and eachincluding a respective second substrate, a respective first antennadisposed on the respective second substrate and configured to radiate arespective first signal having a respective wavelength and a respectivefirst polarization, and a respective second antenna disposed on therespective second substrate and configured to radiate a respectivesecond signal having the respective wavelength and a respective secondpolarization that is approximately orthogonal to the respective firstpolarization.

Example 11 includes the antenna unit of Example 10 wherein the controlmodule includes a control circuit disposed on the first substrate.

Example 12 includes the antenna unit of any of Examples 10-11 wherein:the respective wavelength associated with one of the at least oneantenna module corresponds to a frequency band; and the respectivewavelength associated with another one of the at least one antennamodule corresponds to a different frequency band.

Example 13 includes the antenna unit of any of Examples 10-12 wherein:the controller module includes an approximately planar first conductordisposed on the first substrate; and each antenna module includes arespective approximately planar second conductor disposed on therespective second substrate, and a respective at least one conductivecontact configured to couple, electrically, the respective secondconductor to the first conductor while the antenna module is engagedwith an antenna-module connection region of the controller module.

Example 14 includes the antenna unit of any of Examples 10-13 whereineach of the at least one conductive contact includes a respectiveD-shaped spring contact.

Example 15 includes the antenna unit of any of Examples 10-14 wherein:each of the at least one antenna-module connection region of thecontroller module includes a respective first signal connector; and eachof the at least one antenna module includes a respective second signalconnector configured to engage a first signal connector of thecontroller module.

Example 16 includes the antenna unit of any of Examples 10-15 whereineach of the at least one antenna module is engaged with a respectiveantenna-module connection region of the control module.

Example 17 includes a distributed antenna system, comprising: a masterunit; and at least one remote antenna unit coupled to the master unitand including a control module including a first substrate and at leastone antenna-module connection region; and at least one antenna moduleeach configured to engage one of the at least one antenna-moduleconnection region, and each including a respective second substrate, arespective first antenna disposed on the respective second substrate andconfigured to radiate a respective first signal having a respectivewavelength and a respective first polarization, and a respective secondantenna disposed on the respective second substrate and configured toradiate a respective second signal having the respective wavelength anda respective second polarization that is approximately orthogonal to therespective first polarization.

Example 18 includes the distributed antenna system of Examples 17wherein each of the at least one antenna module is engaged with arespective antenna-module connection region of the control module.

Example 19 includes a method, comprising: radiating, from a firstantenna, a first signal having a wavelength and a first polarization andcarrying data that forms a first portion of a data symbol; andradiating, from a second antenna, a second signal having the wavelength,having a second polarization that is approximately orthogonal to thefirst polarization, and carrying data that forms a second portion of thedata symbol.

Example 20 includes the method of Example 19, wherein: radiating thefirst signal from the first antenna includes radiating the first signalfrom one of a T antenna and an F antenna; radiating the second signalfrom the second antenna includes radiating the second signal from theother one of the T antenna and the F antenna.

Example 21 includes the method of any of Examples 19-20 wherein thefirst antenna is spaced from the second antenna by a distance less thanone half the wavelength.

A number of embodiments of the invention defined by the following claimshave been described. Nevertheless, it will be understood that variousmodifications to the described embodiments may be made without departingfrom the spirit and scope of the claimed invention. Accordingly, otherembodiments are within the scope of the following claims.

The invention claimed is:
 1. An antenna module, comprising: a firstsubstrate; an F antenna disposed on the first substrate and configuredto radiate a first signal having a wavelength and a first polarizationapproximately parallel to the first substrate; and a T antenna disposedon the first substrate and configured to radiate a second signal havingthe wavelength and a second polarization approximately orthogonal to thefirst substrate.
 2. The antenna module of claim 1 wherein the firstsubstrate includes a printed circuit board.
 3. The antenna module ofclaim 1 wherein: the first substrate has an area and a conductive regionthat spans more than half of the area; one of the F and T antennas isdisposed adjacent to the conductive region; and the other of the F and Tantennas is disposed over the conductive region.
 4. The antenna moduleof claim 1 wherein: the F antenna includes a conductive trace disposedon the first substrate; and the T antenna is disposed on a secondsubstrate that is disposed over, and electrically coupled to, the firstsubstrate.
 5. The antenna module of claim 1 wherein the first and secondpolarizations respectively include first and second E-fieldpolarizations.
 6. The antenna module of claim 1 wherein the T antenna isspaced from the F antenna by a distance that is less than one half thewavelength.
 7. An antenna module, comprising: a first substrate havingan area, and a conductive region that spans more than half of the areaand that has an edge; a second substrate that is disposed over, and thatis electrically coupled to the first substrate: an F antenna having aconductive trace disposed on the first substrate and configured toradiate a first signal having a wavelength and a first polarization; anda T antenna disposed on the second substrate over, and at least onefourth the wavelength from the edge of, the conductive region, andconfigured to radiate a second signal having the wavelength and a secondpolarization that is approximately orthogonal to the first polarization.8. An antenna unit, comprising: a control module including a firstsubstrate and at least one antenna-module connection region; and atleast one antenna module each configured for engagement with anantenna-module connection region of the control module, and eachincluding a respective second substrate, a respective F antenna disposedon the respective second substrate and configured to radiate arespective first signal having a respective wavelength and a respectivefirst polarization that is approximately parallel to the respectivesecond substrate, and a respective T antenna disposed on the respectivesecond substrate and configured to radiate a respective second signalhaving the respective wavelength and a respective second polarizationthat is approximately orthogonal to the respective second substrate. 9.The antenna unit of claim 8 wherein the control module includes acontrol circuit disposed on the first substrate.
 10. The antenna unit ofclaim 8 wherein: the respective wavelength associated with one of the atleast one antenna module corresponds to a frequency band; and therespective wavelength associated with another one of the at least oneantenna module corresponds to a different frequency band.
 11. Theantenna unit of claim 8 wherein: the controller module includes anapproximately planar first conductor disposed on the first substrate;and each antenna module includes a respective approximately planarsecond conductor disposed on the respective second substrate, and arespective at least one conductive contact configured to couple,electrically, the respective second conductor to the first conductorwhile the antenna module is engaged with an antenna-module connectionregion of the controller module.
 12. The antenna unit of claim 11wherein each of the at least one conductive contact includes arespective D-shaped spring contact.
 13. The antenna unit of claim 8wherein: each of the at least one antenna-module connection region ofthe controller module includes a respective first signal connector; andeach of the at least one antenna module includes a respective secondsignal connector configured to engage a first signal connector of thecontroller module.
 14. The antenna unit of claim 8 wherein each of theat least one antenna module is engaged with a respective antenna-moduleconnection region of the control module.
 15. A distributed antennasystem, comprising: a master unit; and at least one remote antenna unitcoupled to the master unit and including a control module including afirst substrate and at least one antenna-module connection region; andat least one antenna module each configured to engage one of the atleast one antenna-module connection region, and each including arespective second substrate, a respective F antenna disposed on therespective second substrate and configured to radiate a respective firstsignal having a respective wavelength and a respective firstpolarization approximately parallel to the respective second substrate;and a respective T antenna disposed on the respective second substrateand configured to radiate a respective second signal having therespective wavelength and a respective second polarization that isapproximately orthogonal to the respective second substrate.
 16. Thedistributed antenna system of claim 15 wherein each of the at least oneantenna module is engaged with a respective antenna-module connectionregion of the control module.